Getting unruly consonants like S, K, and T or the hard to hear consonants like F, Z, V, D, L, and P to be coordinated can be problematic, as well. Conductors often have the choir recite the phrases at various tempos while over emphasizing the consonants to practice being concise. Then they try to transfer those techniques to actual singing.
A conductor will want to have good musicians and trained voices in his group, but those singers must learn how to manage their sound quality in order to blend in with the group. They must learn to support their tone quality a little differently in order to blend. The vibrato must be tamed by singing with more breath. The singer must become aware of how to use the light head voice even in the low registers. Those singers will not be happy singing with such control, so the conductor should remember to choose pieces occasionally that will allow those with big voices to let loose and sing with their natural power.
This is tough and takes a lot of practice. It takes the same effort to get the singers to come in together between phrases. Often, the singers relax the rhythm when taking a breath and are late coming in on time in the next phrase. Proper breath management is the key to timing the breaths to fit the rhythm.
The good conductor will always be checking to see if what his group rehearses actually transfers to performance!